Spin system for thermoplastic yarns

ABSTRACT

A spin system for thermoplastic yarns is provided with a melt line, in which the main flow of the melt is transported to a distributor pump. The distributor pump comprises several individual pumps, which divide the main melt flow into several partial flows. Each partial melt flow is supplied to a spinneret. Arranged on one of the driven shafts of the pump are mixing elements. The main melt flow is supplied to the pump via a chamber, in which these mixing elements are arranged.

BACKGROUND OF THE INVENTION

This invention relates to a spin system for thermoplastic yarns as wellas a multiple gear pump with several pairs of gears. Such a spin systemand multiple gear pump are known from U.S. Pat. No. 3,502,033, as wellas DE 19 08 207. In the spinning of thermoplastic yarns, which consistof individual filaments, the thermoplastic material, for example,polyethylene therephthalate, nylon 6, and nylon 6.6, are melted by anextruder, mixed, and then extruded under a high pressure from the mainmelt flow. This main melt flow is subsequently divided into severalpartial melt flows. Each partial melt flow is advanced to a spinneret,from which a plurality of filaments is spun. Thereafter, bundles offilaments are combined to yarns.

For the quality of the product, it is of decisive importance that thefilaments between one another have the same properties. For this reason,special importance is attached to the temperature control in the meltline, which guides the main melt flow, and in the so-called spin head,in which the main melt flow is divided into partial melt flows, and inwhich the partial melt flows are transported to the spinnerets. Likewiseof great importance is the uniform advance of all partial melt flows.For this reason, it is customary to install a multiple gear pump in thespin head. This multiple gear pump receives the main melt flow on theone hand. In the pump, the melt main flow is divided into partial meltflows. The multiple gear pump possesses several individual pumps, whichserve each the purpose of pumping a partial melt flow under a constantpressure and under the same pressure from individual pump to individualpump. It is therefore normal that these individual pumps are driven by acommon drive shaft for all pumps. Known and standard is further the useof gear pumps because of the constancy of the delivery volume anddelivery pressure.

Despite all efforts made to control the temperature and to meter of mainmelt flow and partial melt flows, differences between individualfilaments are found over and over again.

In fact, attempts have become known from time to time, which had beendirected to make the temperature control of the main melt flow uniformby mixing. To this end, the mixer disclosed in DE 12 36 479 B is used.Likewise known are many types of mixers, which are arranged on theextruder or installed as independent mixers in the melt flow (DE 20 30756 C; U.S. Pat. No. 4,253,771; DE 20 40 919 A). However, these measureshave been unable to eliminate the particularly serious problems of auniform control of viscosity and temperature in the spinning ofmultifilament thermoplastic yarns. Likewise, it has not been possible toaccomplish this by a mixer arranged upstream of the nozzle plate, suchas is known from DE 16 60 674 A.

It is the object of the present invention to eliminate such differencesin temperature and viscosity.

This object is accomplished by a spin system including a melt linetransporting a main melt flow from an extruder, and a distributor pumpwhich divides the main melt flow into partial melt flows fordistribution to a spinneret. The distributor pump is preferably amultiple gear pump having several planetary shafts driven by a commondrive shaft. One of the shafts extends into a mixing channel immediatelyupstream of the distributor pump and is provided with mixing elements.Accordingly, the melt is mixed to reduce any temperature gradients justbefore the main melt flow is divided into the partial melt flows.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following an embodiment of the invention is described withreference to FIGS. 1-3. In the drawing:

FIG. 1 is a sectional view of a multiple gear pump in several axialplanes;

FIG. 2 is a schematic top view;

FIG. 3 is a schematic view of a spin system;

FIG. 4 is a sectional view of a multiple gear pump according to anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

To put the invention to practice, it is preferred to use gear pumps. Thegear pump as illustrated comprises a sun gear 1. The sun gear 1 isdriven by a common shaft 2. The drive side is identified by a keyway 3.The sun gear 1 meshes with three planetary gears 4, 5, 6. The planetarygears are distributed over the circumference, each offset by 120°. Theplanetary gears are supported for free rotation about shafts 7. Thisarrangement results in three sets of paired gears, each consisting ofsun gear 1 and one planetary gear. Each of these paired gears forms anindividual pump.

Shown in FIG. 1 is a so-called "six-gear pump", inasmuch as common shaft2 drives a second set of gears, which consists likewise of a sun gear 1and planetary gears 4, 5, 6. For the sake of clarity, it should be notedthat corresponding gears of the two sets of gears are supportedcoaxially. The two sets of gears extend through housing plates 13. Thesehousing plates 13 are provided with cutouts, in which the sun gear andthe planetary gears are arranged. The two sets of gears are separatedfrom one another by an intermediate plate 14. The two sets of gear pumpsare closed, each on their other end side, by cover plates 11 and 15.

The main flow of the thermoplastic melt advancing from the extruderthrough a melt line 8 enters first into an inlet chamber 9 (within thescope of the present application also named mixing chamber anddistributor chamber). The inlet chamber is aligned with one of the pumpshafts in or preceding one of cover plates 11 or 15. These pump shaftsmay be shafts 7, on which the pinions (planetary gears 4, 5, 6) arenonrotatingly supported in this instance, and which are rotatablysupported in the housing. In the illustrated embodiment, it is howeverthe drive shaft 2. To this end, the drive shaft is lengthened, so as toextend beyond the housing width between cover plates 11 and 15. Otherthan in pump layouts known until now, the drive shaft 2 extends throughthe entire housing, and projects with its end facing away from its driveside into inlet chamber 9. Thus, inlet chamber 9 terminates centricallyupstream of housing cover 11. The end of the drive shaft projecting intoinlet chamber 9 is described in the present application as mixing end ormixer shaft 12. The inlet chamber/mixing chamber 9 may extend in coverplate 11, and to this extent, it may form an integral part of the pumpitself. As illustrated in the embodiment of FIG. 1, the inletchamber/mixing chamber 9 forms a part of melt supply line 8, which islocated, for example, in the pump block, to which the pump is attachedby flanges.

From mixing chamber 9 distribution channels 16 extend. Thesedistribution channels 16 extend through cover plate 11, each leading tothe inlet channel 16 of each set of paired gears. The inlet channels ofthe front set of gears, which is adjacent to cover plate 11, also extendthrough intermediate plate 14 in alignment therewith, so as to reachrespective inlets of the second set of gears. Likewise, an outletchannel 17 proceeds from each set of paired gears comprising sun gear 1and one of the planetary gears 4. The outlet channels of the front setof gears, which is adjacent to cover plate 11, leave this set of gearsvia shafts 7 of planetary gears 4 or 5 or 6. The outlet channels 17 ofthe second set of gears extend directly through cover plate 15. Theexact spatial location of the inlet and outlet channels is not shown inthe Figures. It is however known from the prior art, and not shown herein more detail, since it is not subject matter of this invention. Inparticular, it is also possible to arrange the outlets on the inletside. The purpose is to show here only that the invention is to beapplied to multiple gear pumps of any design, provided the condition ismet that the multiple gear pump be operated by a common drive shaft. Themixing shaft 12 or the mixing area of drive shaft 2 may also be arrangedon the drive side. This arrangement may be suitable for reasons ofinstallation, but has the disadvantage that it will require additionalseals. In comparison therewith, the layout in accordance with theillustrated embodiment has the advantage that the advance of the mainmelt flow is not hindered by the technical conditions of the drive. As aresult, the function of the inlet chamber, namely to servesimultaneously as a mixing chamber and a distributor chamber, can besatisfactorily realized in this instance.

The mixing end 12 of the drive shaft is provided with suitable mixingelements. As is shown in the embodiment, pins project radially from thedrive shaft and the cylindrical walls of the mixing chamber. These pinsare arranged in alternating normal planes. These pins which "pass by"relative to one another, perform a thorough mixing of the main melt flowadvancing under pressure through the mixing chamber, before is itsdivided into partial melt flows. Likewise, other mixing elements onmixing segment 12 of drive shaft 2 and/or on the walls of the mixingchamber are conceivable and described in the prior art.

The use of the drive shaft as a mixing shaft and the intensive mixing ofthe main melt flow directly before it is divided into partial melt flowscauses that all cross sectional areas of the main melt flow are mixedwith one another. It is precluded that possible viscosity andtemperature gradients become again noticeable between the individualcross sectional areas upon dividing the main melt flow into partialflows. It is thus accomplished that all partial melt flows arehomogeneous not only in themselves, but also between one another, andthat they have a uniform temperature and viscosity.

Illustrated in FIG. 3 is a spin system. Same comprises an extruder, inwhich a thermoplastic material is melted and discharged under pressureinto the melt line 8. The melt line leads into the spin head. In thespin head, the melt line is connected to the multiple gear pump inaccordance with this invention, and the main melt flow is divided bythis pump into partial flows. Each partial melt flow is then supplied toa spinneret. From the spinneret, a plurality of multifilament yarns isspun. Each yarn is withdrawn by a godet and subsequently processedand/or wound.

Shown in FIG. 4 is a multiple gear pump, which corresponds to theembodiment of FIGS. 1-2, except the following deviations. With theexception of these deviations, the description of FIGS. 1-2 is herewithincorporated by reference. The drive shaft terminates in a blind hole inhousing cover 11. The pump is flanged to a pump block 20. The pump blockwith the pump flanged thereto is arranged in spin box 21 of FIG. 3. Theso-called planetary gears are nonrotatingly supported on theirrespective shafts 7. The shafts 7 are again rotatably supported inhousing plates 11, 14, 15. A shaft 7.1 projects from the housing, namelyfrom cover plate 11, and extends into inlet channel 9. The last segmentof inlet channel 9 forms the mixing chamber, which is located in thisinstance exclusively in the pump block. The peripheral wall of themixing chamber and/or shaft 7.1 are provided with mixing elements of aknown design, in the present embodiment pins. From mixing chamber 9,distributor channels branch off, which extend to the inlet end of eachpump pairing. In this embodiment, all outlet channels are arranged onthe flange side of the pump and extend through the pump block to theindividual spinnerets shown in FIG. 3.

We claim:
 1. A spin system for thermoplastic yarns, comprising:a melt line in which a main flow of a thermoplastic melt is transported under pressure from an extruder; a distributor pump downstream from the melt line for receiving an entering main melt flow and having a common drive shaft, the distributor pump comprising a plurality of distribution channels which divide the entering main melt flow into partial melt flows, and a plurality of individual pumps which each receive a partial melt flow from the distribution channels and which each include a planetary shaft driven by the common drive shaft, and a mixing channel in alignment with one of the common drive shaft or a planetary shaft, an upstream portion of which shaft extends into the mixing channel and which portion is provided with mixing elements; and a spinneret downstream of the distributor pump, for spinning a bundle of filaments, which receives a partial melt flow discharged from one of the individual pumps.
 2. A spin system as in claim 1 wherein the shaft extending into the mixing channel is the drive shaft.
 3. A spin system as in claim 2 wherein the distributor pump further comprises a mixing side adjacent to the mixing channel and an opposite drive side from which the drive shaft is driven.
 4. A spin system as in claim 3 wherein the distributor pump further comprises a housing and wherein the mixing channel is defined in part by the housing.
 5. A spin system as in claim 1 further comprising a pump block to which the distributor pump is flanged and in which the melt line and the distribution channels extend, and wherein the mixing channel extends at least partly into the pump block.
 6. A multiple gear pump for distributing a melt flow of thermoplastic material received from a pressurized melt line, the pump comprising:a plurality of sets of paired gears mounted on respective planetary shafts; a common drive shaft in operative connection with each of the planetary shafts; a mixing chamber for receiving a main melt flow from a melt line; and a plurality of distribution channels extending from the mixing chamber to a respective set of paired gears such that the main melt flow is divided into a plurality of partial melt flows; wherein one of the common drive shaft or a planetary shaft extends into the mixing chamber and mixes the melt flow before it is divided into the partial melt flows.
 7. A multiple gear pump as in claim 6 wherein the shaft extending into the mixing chamber is the common drive shaft. 